Shaolin Yijinjing and marrow washing are both good fitness exercises, but now this thing is too mysterious to be sold as a secret book of Wulin. It's actually quite simple. I recommend watching Yong Yang's Zhu Zhangsha's Body-building Exercise, in which the ten tricks of tiger and dragon are all easy to muscle and wash the marrow.

Here's another way-live horse stake:

Open your feet three feet in parallel and squat slowly until your thighs are flat with the ground. Remember to be slow. Then stand up slowly, slowly. This is the first achievement. Practice hard.

After a period of time, the second step is feasible, exhaling when squatting and inhaling when getting up. Breathe, breathe, and fall together. Remember, still slow.

Give it a try and you'll know.